Addressing structural uncertainty: A case study of fault timing in the Perth Basin

Structural uncertainty is not often explored during the groundwater modelling process, despite being one of the major sources of uncertainty. Whilst considerable effort has been recently made towards reducing and quantifying parameter uncertainty, relatively little has focused on structural error mostly likely due to the gruelling nature of geological modelling and its early position in the modelling workflow. Faults represent a major source of structural uncertainty and can fundamentally change a groundwater flow regime through fault zone permeability modification and stratigraphy warping and offsetting. Understanding fault type and timing is critical for predicting groundwater flow, as the offset of aquitards may result in hydraulic connection of otherwise vertically isolated aquifers. Although downhole geophysics and palynology assist in understanding sedimentary architecture, there always remains uncertainty in fault architecture without adequate seismic data. The purpose of this research is to promote the importance of structural uncertainty in groundwater models, in particular the effect of fault configuration and timing on long term groundwater flow predictions.